Material for commutator brushes



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F. c. ATKINSON MATERIAL FOR COMMUTATOR BRUSHES Filed April 25, 1923 ,fj--EUPPERMEARBDN gnwntoz FREDERICK C. ATKINSON, OF INDIANAPOLIS, INDIANA.

MATERIAL FOR OMM'UTATOR BRUSES.

Application iiled April 25, 1923.` Serial No. 634,631.

. a substance .for use as an .electrical conductor, for use particularly in the manufacture of commutator brushes for electric motorsY and generators, which should consist essentially of carbon intimately mixed with metallic copper or other metals or alloys of proper conductivity in the form of firm blocks, rods or sticks. The requirements of the metal used in combination with the carbon are ,not necessarily high conductivity of the metal alone, but it must give a combination with carbon that readily conducts the electric current. e

I prefer to use copper inasmuch as copper usually gives a brush of the necessary properties, but inasmuch as silver or nickel, or combinations of silver and nickel, or combinations of either or both with copper or with zincor with othermetals may give a satisfactory brush, I do not limit the scope of my invention to copper, or'even to the metals that are when used alone good conductors of electric current. p

My invention does not concern itself with the presssing 'of this mixture of carbonA and metal into sticks as this is in a very advanced stage of the art. But my invention has for its object the production of carbon and metal in a finely divided state, ready for molding into homogeneous sticks. To accomplish this object I make use of copper oxide, either the cuprous or cupric oxide, together with some variety of pitch which on destructively distilling will yield carbon as a residue.

By this method I can produce a mixture of carbon and copper in a most any proportion desired from zero percent copper to 85 per cent or even 90 per cent copper, and from 100 carbon to l5 or even 10 per cent carbon. Ordinarily it is desired to have a fairly high proportion of copper inv this mixture 'so that the final brush produced by molding this mixture into a stick has suficient metal content to give a high conductivity or low voltage drop.

The single figure of the drawingV shows a brush made vaccording to my invention.

In carrying out this invention I reduce the co per'oxidesand the pitch to a nely divided state, and mix them in the necessary proportion to yield the proportion of metal and carbon desired. When the cupric oxide is used I am obliged to use a larger quantity of it with relation to the quantity of pitch used on account of the lower copper content of this oxide, cupric oxide containlng only about 8O per cent copper theoretically, whereas the cuprous oxide contains 88-8/10 per cent metallic copper theoretically. After the necessary quantity of metallic oxide and pitch have been thoroughly blended either by mechanical mixture or by grinding 1n a ball orppebble mill the mixture 1s transferred to a suitable still for destruct1ve distillation, heat is applied las is ordinar1ly done in distilling pitch alone, the pltch itself fuses and completely envelops thel copper.` It yields some volatile matter, which volatile matter is condensed and may be used for similar purposes as pitch distillates are usually employed. The yield, of distillates, however, is lower in this instance than when pitch is distilled alone due to the oxygen yielded by the copper oxide which oxygen oxidizes a portion of the pitch distillate to carbon-monoxide or carbon-dioxide and possibly other more complex compounds. The copper oxide is thus reduced to the elementar or metallic state thus producing 'metal 1n a finely divided form from the metallic oxides. The pitch yields reducing substances for the production of metal from metallic oxides and carbon. The carbon in Htl this form serves as a matrix and carries the fine particles of metal in their nascent state.

By the term pitch as used in this paper I refer to such substancesfas the residue left from the distillation of coal tar or petroleum or wood resin, or any other tarry matter, f

or any organic substance which will onA heatlng to the point of distillation together with lmetallic oxides produce carbon' and at the Sametime reduce the metallic oxides to the elementary or metallic state. Or I may mix the metallic oxide with powdered coal, especially bituminous coal.

I have found for example that copper oxide and fatty oils, when distilled in this fashion, will produce a mixture of'rcarbon and metal, or I have prepared this combina-` tion of metal and carbon by precipitating metallic soaps as copper palmitate produced by precipitating ordinarysoap by means of soluble copper salts. However, I do not lconsider this as economical fromxthe standpoint of raw materials, or from the standpoint of cost of .operation, and therefore precfer the use of pitch together with metallic 0x1 e. I

I do notlclaim anything new or novel 'and the pitch used in 'this process, while there may be desirable products produced from said pitches distilled by this process, which are not produced when the pitches are distilled by the usual'process, yet I do not consider that such. come within the scope ofy this invention, but what I do claim as new and patentable and means to come within the scope of this invention is the mixture of carbon, and metallic copper or carbon and other metal or metals.

When carbon or such mixtures as metal and carbon are pressed into sticks they require a bindingl material, which binding material is baked out after the mixture has been formed into a solid block by reason of the high pressure to which it is subjected; ordinarily some form of pitch is used as this binding material, and as the process of bak# ingproceeds the volatile matters of the pitch are driven ed and part of the pitch is carbonized. In making a commutator brush, from my mixture of carbon and metal which has been ground or otherwise reduced to powder or at least to sucha finely divided `condition as to providel fragments of convenient size for molding, it is very obvious that the carbon content of the iinal brush would bevhigher than the carbon content of the mixture of metal and carbon used for making this block or stick. However, it deto this pitch to maintain the desired ratio of copper to carbon; or we may even use finely divided copper or bronze for this purpose. When the final block is subjected to the baking temperature 'this copper oxide is reduced to a metallic or elementary state at the same time that 'the pitch is carbonized by interaction of the oxidizing property of the metallic -oxide and the reducing property of the pitch. A

Having thus fully described my said invention, what I claim as new and desire to secure by Letters Patent, is:

l. The .method of preparing conducting material for electricity comprising the steps of combining an oxide of copper with fusible material of organic origin, subjecting the mixture to destructive distillation, cooling the product, reducing it to a finely powdered condition, adding a binder containing copper, molding the mixture into desired form, and thereafter baking, substantially as set forth. n

2. The method of preparing conducting material 'for electricity comprising the steps of mixing a metallic oxide with organic material, subjecting the mixture to destructive distillation, reducing the` product to a finely divided condition, adding a binder including metallic material, molding the mixture into desired form, and thereafter haking, substantially as set Jforth.

In witness whereof, I have hereunto set my hand at Indianapolis, Indiana, this 14th day of April, A. l). nineteen hundred and twenty-three.

FREDERICK C. ATKINSON. 

